I am keen to check this out since I really want to keep my ISO at 125 as much as possible. Despite the fact that ISO 200 is the real base ISO and there are all sorts of warnings about poor dynamic range if the lower setting is used, as before with the Olympus PEN's I had that gave this option, I don't had a problem with it. And there is a difference. Just like on the Olympus cameras the lower setting on the GH3 produces a noticeably cleaner file, with no luminance noise, which is present even at ISO 200. I believe m4/3 cameras used to do this thing whereby they underexposed by a stop to protect the highlights and then use in camera software the lighten the shadows. This on both raw and jpg files. I can't say whether they still do this and whether or not the lowest ISO 100 /125 performs this process or not.
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